Composition and device for creating an underwater cloud



May 2, 1967 J. A; GRAND COMPOSITION AND DEVICE FOR CREATING AN UNDERWATER CLOUD Filed April 28, 1944 PERSISTENCE OF BUBBLE CLOUD L0 BUBBLE DIAMETER IN GM.

m "a m m m 5 o Omm \20 Z mmE O wh JOSEPH A. GRAND United States Patent 3,316,840 COMPOSITION AND DEVICE FOR CREATING AN UNDERWATER CLOUD Joseph A. Grand, Washington, D.C., assignor to the United States of America as represented by the Secretary of the Navy Filed Apr. 28, 1944, Ser. No. 533,199 6 Claims. (Cl. 102-66) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

My invention relates to underwater sonic ranging and more particularly to countermeasures against such ranging. My invention is especially directed to a composition and a device for use with said composition to produce echoes simulating those obtained from submarines and thus confounding detection.

Sonic detection of submarines by surface craft depends on the receipt of echoes from the submarine hull of timed signals, preferably of supersonic frequency, sent out by the surface craft. Due to the highly directional characteristics of supersonic waves in water, it is possible to determine the direction and range of a submarine and to locate it by means of these signals.

It is well known that echoes are obtained from other sources than solid bodies submerged in the water. A common source of such echoes is any sizable area of the sea in which the effective density of the water changes suddenly. Thus it might be said that the boundary between two portions of the sea of appreciable difference in density acts as a reflecting surface for sound signals. Such echoes are most commonly obtained from the boundaries of warm and cold currents. Sometimes they are obtained from a turbulent area such as a whirlpool or propeller wake of a vessel in a substantially still surrounding body of water.

It has long been recognized by Naval personnel that some simple means of artifically producing an underwater reflecting boundary would be of great tactical value in submarine warfare.

It is an object of my invention to provide a means for changing the effective density of a large volume of water to produce a reflecting boundary for sonic and supersonic signals.

A second object of my invention is to provide a com position of matter adapted to react with water to produce a large volume of gas in the form of fine bubbles to form an underwater cloud or boundary.

A third object of my invention is to provide means for laying down the underwater cloud at a distance from the submarine. The purpose of laying down the cloud at a distance from the submarine is to give enemy detection apparatus a false indication suflicient to keep the first volley of depth charges at a safe distance from the pursued submarine. It is of vital importance to the pursued that the first volley miss the genuine target for once depth charges explode under water, the surrounding area for a considerable distance remains so badly disturbed thatfurther ranging is impossible for a long period of time. The

pursued submarine, if not injured by the initial volley, is thus given time to escape.

Other objects of my invention will in part be obvious and will in part appear hereinafter in the detailed description when considered in connection with the accompanying drawings, where:

FIG. 1 is a plot of the rate of rise of gas bubbles as a function of bubble size, and

FIG. 2 represents a simplified longitudinal section of a shell embodying my invention.

'in the deep water.

In order to confuse a skilled operator sufliciently to mistake an echo from an underwater cloud for an echo from the hull of a submarine, it is necessary to produce a large cloud of fine bubbles quickly at a distance from the submarine. The device for generating the cloud must be small, light and substantially nonhazardous to personnel, particularly if it should be accidentially operated in a submerged submarine.

It is well to point out here that generation of an ordinary mass of bubbles is quite a simple matter. The number of compositions which will generate a gas upon reaction with water is legion. To give a strong metallic echo, however, the bubble cloud must be composed of fine bubbles and the cloud must be persistent. Experiments and theoretical considerations have shown that bubbles of a given size have, approximately at least, a resonant frequency given by the following relationship where f is the frequency, r the bubble radius, K the ratio of the two specific heats of the gas in the bubble, P the hydrostatic pressure on the bubble, and d the density of the water. The metallic quality and intensity of the echo obtained from a bubble cloud will be improved the closer the frequency of the signal is to the resonant frequency of the bubbles.

A second consideration involved in the production of submarine-simulating echoes is the production of a relatively persistent cloud of bubbles. This depends on several factors, namely, the rate of rise of the bubbles, their initial depth and their rate of solution in the surrounding water.

Rate of rise of the bubbles is a function of bubble size as can be seen by reference to the graph given as FIG. 1 of the drawing. It is apparent that the rate of rise of bubbles is quite slow only with very fine bubbles, that it increases very rapidly with diameter at first and then levels oif. Evidently a satisfactory underwater cloud must be composed of very fine bubbles.

The initial depth of the bubble is arbitrarily controllable and in the case of a submarine generating a cloud, it would be approximately that of the submarine.

The solution rate of the bubble, within limits, is a linear function of hydrostatic pressure. Also, within limits, the solubility of a gas used to form an underwater cloud would be advantageous in that solution of part of the gas would decrease the size of the bubble and thus series of problems involving bubble size, solution rate and rate of riseis encountered.

Obviously it is just about impossible to produce a cloud:

It is possible, however, at

of uniformly fine bubbles. least to approach this condition sufliciently to give a long persistent cloud as my studies have revealed.

. My solution to the problem of producing an underwater cloud, which comprises my invention, contemplates the use of a small projectile suitable for ejection under water, which, after a predetermined time, will open and permit its contents to react with the water. The reaction is one which will produce copious quantities of gas and by virtue I of its rapidity a large cloud of bubbles is quickly generated. The fine bubbles produced do not diffuse rapidly Consequently within a few seconds after the opening of the shell a large cloud of bubbles appears in the water and the effective density of the water in the immediate vicinity of the opened projectile is reduced. Within a short time the cloud of bubbles is large enough and dense enough to give an echo comparable to that obtained from a submarine.

More specifically I use a small shell, of standard signal type, loaded with a gas generating composition which may include a wetting agent and a binder. In the shell is also included a time fuze and an ejecting charge.

The gas generating composition can be any compound, mixture of compounds, metal, amalgam, or alloy which upon contact with water will react rapidly to produce a gas of low solubility in water. In addition the compound used should be light, non-hazardous for handling and preferably should generate a copious quantity of non hazardous gas per unit weight used. In my invention I-have found that compositions which generate hydrogen are satisfactory gas generators. Hydrogen is a good gas to generate for it is substantially non-hazardous to personnel and compounds generating it are common. Specifically, alkali metal hydrides are very advantageous. Other compositions that can be used quite successfully are alkaline earth metal hydrides, alkali metal borohydrides, alkaline earth metal borohydrides, mixtures of dry alkali hydroxides and amphoteric metals (e.g. A1, Zn), amalgams of metals reactable with water, alloys of alkali metals, alloys of alkaline earth metals, alloys of alkali and alkaline earth metals and alloys of alkaline earth metals with amphoteric metals (e.g. Ca-Zn alloys). One of the prime considerations in selecting a gas generator is to select the one giving a large volume of gas per unit weight and volume of material. Rate of reaction is generally a problem in a negative sense, that is, usually it is necessary to slow the reaction when some of the more active metals are employed. I have found alkali metal hydrides and borohydrides especially satisfactory from the standpoint of reaction rate and volume of gas produced.

The compositions mentioned above are all hydrogen generating but it need not be assumed that hydrogen is the only usable gas. One could, for example, load a shell with aluminum carbide (Al C which would generate methane upon contact with the water. Likewise alkali metal and alkaline earth metal peroxides could be used to generate oxygen. The two most serious limiting factors on the composition used are the solubility in the water of the gas generated and the availability of the compound.

The operation of my invention can be more clearly understood by reference to the drawings.

In thevdrawing, the shell is represented as comprising a case equipped with conventional firing means 11, a time fuze 12 and expellant charge 13. Within the case 10 and ahead of the expellant charge 13 a plurality of containers 14 (six shown) which are open at their forward ends. The shell is closed by means of a nose 15 which fastens onto the end of the case 10 and retains containers 14 in place by means of a group of cardboard discs 16. The containers 14 are packed with a mixture of hydrogen generating material such as an alkali metal hydride mixed with an inert binder such as paraffin which aids in controlling the reaction rate and in controlling the bubble size as explained in more detail below. A small weight such as a lead pellet 17 is placed in each container to help adjust the specific gravity of the mass to a value slightly greater than that of the water to avoid having the material surface.

When the shell is expelled from the submarine the time 12 is ignited by means of the firing mechanism 11 and after a suitable time, set by the time fuze, the expellant charge 13 bursts tainers 14 in the water. The bubble cloud starts to form as soon as the open containers contact the water.

In accordance with my invention the containers 14 are packed with a mixture of gas generating material the shell and scatters the con-.

and an inert binder with a wetting agent if desired. The binder and gas generator are mixed together and pressed into the container in such proportion that the reaction gives a large cloud of bubbles in thirty seconds and the bubble size is such that the cloud persists for at least ten minutes. The inert material may be a wax or thermoplastic resin of almost any kind, for example beeswax, ceresin, carnauba, paraffin, polystyrene or a methacrylate resin provided it does not react appreciably with the active ingredient during storage.

Satisfactory fillers can be prepared according to my invention as follows:

Example 1 Lithium hydride, preferably divided finely enough to pass at least a No. 3 mesh screen, is mixed with paraffin at a temperature slightly above the melting point of the paraffin. The mixture is allowed to cool sufficiently to solidify and then passed into containers. Generally proportions within the range of about 10% to about 50% of the binder and the rest lithium hydride are suitable. An optimum composition which gave a long-persistent cloud was found containing about 20% paraffin and about lithium hydride. High melting paraffins are preferred for they permit flaking of particles during reaction. Paraffin was the best of the waxes for it showed no tendency to react with the hydride.

Example 2 The proportions of lithium hydride as in Example 1 mixed with any natural wax give comparable results but suffer the disadvantagethat the natural waxes react slowly with the hydrides.

Example 3 The proportions of lithium hydride as in Example 1 mixed with a powdered thermoplastic resin and pressed into a cake (with just sufficient heating to bind the resin) gives comparable results.

Example 4 Any of the hydrogen generating compositions mentioned above, particularly the alkali metal hydrides or borohydrides, can be substituted for the lithium hydride. In each individual case, variation of proportion of gas generator is needed to compensate for slightly slower or faster reaction. The necessary variation is readily determined by preparing a few sample pellets.

Example 5 In any of the receding examples, the quality of the cloud is improved by including in the composition a small proportion of wetting agent. Its action is such that it lowers the surface tension of water adjacent to reacting particles and thus permits smaller bubbles of gas to be disengaged from the reacting mass. I have found that about 1% of a wetting agent (one which will not react with the active ingredient) by weight makes for more uniform bubble size and gives a more uniform reaction time over a range of temperatures. A particularly good one to use in the lithium pellet described in Example 1 is sodium isopropyl naphthalene sulfonate commonly called Aerosol OS.

Since certain changes may be made in the above composition and modifications effected in the device for using it without departing from the scope of the invention,.it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

Having described my invention, what I claim as new and desire to secure by Letters Patent is:

1. A device capable of generating an underwater cloud which comprises a shell, a fuze and an expellant charge in said shell, a charge for said shell comprising a gas generating material so arranged that ignition of said expellant charge expels said gas generating material, said gas generating material comprising an intimate mixture of alkali metal hydride and a binder.

2. A device capable of generating an underwater cloud which comprises a shell, a fuze and an expellant charge in said shell, a charge for said shell comprising a gas generating material so arranged that ignition of said expellant charge expels said gas generating material, said gas generating material comprising an intimate mixture of alkali metal hydride, a wetting agent and a binder.

3. A device capable of generating an underwater cloud which comprises in combination in a shell, a fuze, an expellant charge and a series of units each comprising an open container carrying a material capable of rapidly reacting with water to generate gas of low solubility in water, said units having a specific gravity slightly greater than that of the water and being arranged in the shell so as to be ejected therefrom on detonation of the expellant charge.

4. A device as defined in claim 3, wherein the units are in aligned relationship.

References Cited by the Examiner UNITED STATES PATENTS 735,299 8/ 1903 Reichenau l02--66 909,536 1/1909 Brindley 252-188 910,942 l/ 1909 McCombie. 1,394,335 10/ 1921 Nichols 102-60 1,417,475 5/1922 Weeke 10Q66 BENJAMIN A. BORCHELT, Primary Examiner.

A. BISHOFF, ARTHUR M. HORTON, SAMUEL BOYD, Examiners.

L. H. MEYERS, W. KUJAWA, Assistant Examiners. 

1. A DEVICE CAPABLE OF GENERATING AN UNDERWATER CLOUD WHICH COMPRISES A SHELL, A FUZE AND AN EXPELLANT CHARGE IN SAID SHELL, A CHARGE FOR SAID SHELL COMPRISING A GAS GENERATING MATERIAL SO ARRANGED THAT IGNITION OF SAID EXPELLANT CHARGE EXPELS SAID GAS GENERATING MATERIAL, SAID GAS GENERATING MATERIAL COMPRISING AN INTIMATE MIXTURE OF ALKALI METAL HYDRIDE AND A BINDER. 